An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during an impact. As opposed to deploying air bag cushions through various openings, active bolsters use an interior trim surface as part of the bolster which expands at the beginning of an impact event and absorbs the passenger impact and dissipates energy through the action of an inflation gas.
In a typical structure, an active bolster includes a front wall or panel that faces a vehicle occupant and is attached to a rear wall or panel along a sealed peripheral seam. The walls are typically made of molded plastic with an accordion section that straightens during deployment, thereby providing an inflatable bladder. The peripheral seam is formed by hot welding, for example.
It is desirable to vent the inflatable bladder at all times to maintain it at substantially atmospheric pressure during non-impact conditions. Otherwise, noticeable deformation of the interior trim component incorporating the active bolster may occur during temperature extremes since the wall materials are relatively flexible. While venting is needed, it is desirable to avoid the use of expensive, complicated exhaust valves. A common solution has been to provide a continuously open vent of a fixed flow area. The vent flow area must be large enough to provide sufficient exhaust of gas to enable the desired cushioning effect during an impact.